I believe Phil is spot on about the reason for blocking out the license plate in photos. If you post a picture with your plate number, I can get lots of sensitive information about you that you might not want people to know, like your home address, driving history and much more. I would imagine that if someone wanted to dupe my tag, it would be much easier to just write it down as I drive past them than to wait for me to post a picture on the net
But regardless of the reason, it's still a good idea to blank out or otherwise obscure the plate in photos, particularly those you are going to put out on the net for the whole world to see.
Cheers,
Brad
